Besides the small detail that I don't believe in prophetic dreams, there is one way to look at it: Does the dream express a fear that you have, symbolically or even directly? Does this 'brother aspect' of yours mirror something that is now happening in your life, or does the fear of losing him happen to be something you've been thinking about? If you can find correlations with your waking life, I'd go with the symbolism of dreams.
And yes, don't be shocked, I actually don't believe in something.